I have a little (big) problem with the latest Xcode (4.5), OSX 10.8.2 and develop VST Plugins.
Everything seems to work fine, compile without errors.
Except one thing: the compiled plugins won't load in VST Host (Cubase 6).
Had any other developer the same problems with Xcode 4.5? And how did you fixed it?

btw: in the past I was using Xcode 3.0 and OSX 10.5.8 -> everything worked fine...

I'm having no problem with making VST plugins in Xcode 4.5 (also 10.8.2).
Does the plugin at least show up in the list in your host, or is it totally absent? It's a little hard to know what the problem may be with so little info.

Semantic Issue Group/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1217:35: Use of undeclared identifier 'QDSwapPort'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1230:8: Use of undeclared identifier 'QDSwapPort'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1304:6: Use of undeclared identifier 'QDGlobalToLocalPoint'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1338:25: Use of undeclared identifier 'QDSwapPort'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1351:7: Use of undeclared identifier 'QDSwapPort'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1493:4: Use of undeclared identifier 'GetFNum'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1539:17: No viable conversion from 'RGBColor *' to 'CColor'/vstsdk2.4/vstgui.sf/vstgui/vstgui.h:280:8: Candidate constructor (the implicit copy constructor) not viable: no known conversion from 'RGBColor *' to 'const CColor &' for 1st argument; /vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:825:42: Passing argument to parameter 'color' here/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1540:3: Use of undeclared identifier 'RGBForeColor'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1567:3: Use of undeclared identifier 'GetFNum'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:3559:2: Use of undeclared identifier 'GetRegionBounds'/vstsdk2.4/vstgui.sf/vstgui/vstcontrols.cpp:1307:10: No matching function for call to 'PinRect'/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.8.sdk/System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/Headers/MacWindows.h:10483:1: Candidate function not viable: no known conversion from 'Point' to 'const Rect *' for 1st argument;

/Users/---/Downloads/samples/vst2.x/mac/lib/cview.cpp/Users/---/Downloads/samples/vst2.x/mac/lib/cview.cpp:661:22: No matching function for call to 'make_pair'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/macfileselector.mm/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/macfileselector.mm:239:5: 'beginSheetForDirectory:file:types:modalForWindow:modalDelegate:didEndSelector:contextInfo:' is deprecated/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/macfileselector.mm:244:21: 'runModalForDirectory:file:types:' is deprecated/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/macfileselector.mm:255:5: 'beginSheetForDirectory:file:modalForWindow:modalDelegate:didEndSelector:contextInfo:' is deprecated/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/macfileselector.mm:260:21: 'runModalForDirectory:file:' is deprecated/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:493:4: Use of undeclared identifier 'GetPortBounds'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:524:2: Use of undeclared identifier 'GetPortBounds'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:539:24: Use of undeclared identifier 'QDSwapPort'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:542:3: Use of undeclared identifier 'QDSwapPort'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:747:13: Enumeration value 'kError' not handled in switch/Users/----/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:808:24: Use of undeclared identifier 'NewRgn'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:822:5: Use of undeclared identifier 'DisposeRgn'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:1016:17: Use of undeclared identifier 'kQDRegionToRectsMsgParse'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewframe.cpp:1117:37: Use of undeclared identifier 'kQDParseRegionFromTopLeft'/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewoptionmenu.cpp/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewoptionmenu.cpp:107:17: 'UniqueID' is deprecated: first deprecated in Mac OS X 10.8/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewtextedit.cpp/Users/---/Downloads/samples/vst2.x/mac/lib/platform/mac/carbon/hiviewtextedit.cpp:111:3: Use of undeclared identifier 'GetFNum'

So, I have no idea WHY! Followed all the steps in the documentation from VSTGUI.
Any ideas?

I'm quite sure, as is evidenced by your output, that VSTGUI 4 also needs the 10.6 SDK. If you have Xcode 3 lying around, grab the 10.6 SDK from it and place it inside the Xcode 4 bundle (in /Developer/Platform/MacOSX/Developer/SDKs I think). Then you can choose 10.6 as the base SDK in Xcode 4.5.

Thanks all. Solved the problem.
I don't know how, but it works now with the vstgui.sf from steinberg sdk.
Xcode is strange different to all the other Ide.
Maybe it was really the 10.6 sdk. I'm not sure...